Search Results (1,737)

In this study, laser powder bed fusion (PBF-LB) 022Cr17Ni12Mo2 steel plates with dimensions of 50 mm × 50 mm × 2 mm were fabricated using a laser power of 206 W, a scanning speed of 900 mm/s, a hatch spacing of 90 μm, a layer thickness of 30 μm, and an interlayer scanning rotation of 67°. The specimens were then subjected to solution treatment at 900–1100 °C for 30 min and at 950 °C for 30–120 min. Unlike previous ultrasonic studies on additively manufactured metals, which mainly focused on defect detection, elastic-constant characterization, or residual stress evaluation, this work investigates whether solution-treatment-induced changes in grain size and dislocation density can be quantitatively reflected by laser-ultrasonic attenuation and further correlated with yield strength. Laser ultrasonic nondestructive testing using a 1064 nm pulsed laser with a pulse width of 8 ns and a pulse energy of 500 mJ was combined with metallographic observation, EBSD characterization, XRD analysis, tensile testing, and microhardness measurement. The results show that the solution-treated samples retained a single-phase γ-austenitic structure, while microstructural recovery, weakening of PBF-LB-induced cellular substructures, and partial annihilation of cell-wall dislocations led to a reduction in KAM-derived dislocation density from 2.04 × 10¹⁴ m⁻² to 1.45 × 10¹⁴ m⁻² and a decrease in yield strength from 466.9 MPa to 407.4 MPa. Within the present dataset, the EBSD-equivalent grain size showed an apparent positive correlation with ultrasonic attenuation, while the KAM-derived dislocation density showed an empirical negative correlation with ultrasonic attenuation. However, ultrasonic attenuation should be interpreted as a combined microstructure-sensitive response rather than as a response controlled only by EBSD-equivalent grain size or dislocation density. Based on the empirical correlations among ultrasonic attenuation, EBSD-equivalent grain size, KAM-derived dislocation density, and yield strength, a preliminary attenuation-based calibration model was established for the present solution-treated samples. The model should be regarded as an in-sample empirical calibration within the present experimental range rather than a general Hall–Petch-based predictive model. The model showed good in-sample fitting performance, with (R²) values higher than 0.85 and a maximum in-sample fitting error of 3.85%. However, because the model was established and assessed using the same eight solution-treatment conditions, it should be regarded as a preliminary calibration model within the present experimental range rather than a general predictive model. This study demonstrates the potential of laser ultrasonic attenuation for non-contact evaluation of microstructural and mechanical-property variations in solution-treated PBF-LB 022Cr17Ni12Mo2 steel. Full article

Fe-Al intermetallic coatings were fabricated on 0Cr21Al6Nb stainless steel by pack cementation to systematically investigate the effects of temperature (650–800 °C) and holding time (2–16 h) on the coating microstructure, phase constitution, and hardness. The coatings primarily consisted of Fe₂Al₅, with a minor amount of FeAl₃ confined to the outermost surface. The coating/substrate interface exhibited a characteristic serrated or tongue-like morphology, which became increasingly pronounced with increasing temperature and holding time, indicating enhanced interdiffusion across the interface. Both increasing temperature and prolonging holding time markedly promoted coating growth and increased the coating thickness, while simultaneously facilitating the enrichment of FeAl₃ in the near-surface region. Despite these microstructural variations, the coating hardness remained relatively stable at approximately 960 HV, which was substantially higher than that of the substrate; meanwhile, the substrate exhibited a slight reduction in hardness after aluminizing. Thermodynamic analysis revealed that Fe₂Al₅ was preferentially formed owing to its relatively lower Gibbs free energy, and its formation remained thermodynamically favored during subsequent coating growth, whereas FeAl₃ was restricted to the coating surface. Kinetic analysis demonstrated that coating growth followed a parabolic law, indicating a diffusion-controlled growth mechanism, with an apparent activation energy of 107.5 kJ·mol⁻¹ for Al diffusion. Furthermore, temperature exerted a more pronounced influence on coating growth than holding time, highlighting temperature as the dominant kinetic parameter governing the formation and thickening of the Fe-Al intermetallic coating. Full article

Grain boundaries (GBs) are important recombination-active defects in polycrystalline and multicrystalline silicon solar cells, but the effects of their electrical activity, geometry, and spatial arrangement are often difficult to separate. In this work, two-dimensional (2D) drift–diffusion simulations are used to investigate how GB trap density, carrier capture cross-section, orientation, length, number, and network geometry affect silicon solar-cell performance. A controlled comparison between rotating GBs whose length changes with angle and fixed-length GBs shows that the strong apparent orientation dependence is dominated by the accompanying variation in active GB length. When the GB length is fixed at 100 μm, the variations in short-circuit current density ($J_{\mathrm{sc}}$), open-circuit voltage ($V_{\mathrm{oc}}$), efficiency, and fill factor are comparatively small. As a second contribution, irregular polycrystalline microstructures are generated by Voronoi tessellation, producing distributions of grain sizes, shapes, boundary lengths, and junctions that are more representative than simplified structures based on isolated or regularly spaced boundaries. These networks are used to connect grain size, total electrically active GB length, recombination, local electric fields, carrier-flow redistribution, and device performance. As the characteristic grain size increases from 5 to 100 μm, $J_{\mathrm{sc}}$ rises from 15 to $34\mathrm{mA}{\mathrm{cm}}^{-2}$, $V_{\mathrm{oc}}$ from $0.54$ to above $0.61$ V, and the power conversion efficiency from $6.5\%$ to $17\%$. GB-induced photovoltaic loss is therefore governed not by GB number or nominal orientation alone, but by the combined effects of electrical activity, total active boundary length, and network geometry. Full article

The accurate evaluation of gastrointestinal (GI) diseases such as celiac disease (CeD) relies on the assessment of villous architecture, yet progress in imaging-based diagnostics, particularly video capsule endoscopy (VCE), is constrained by the absence of anatomically realistic and reproducible physical models of the intestinal mucosa. Existing benchtop phantoms typically reproduce gross luminal curvature but fail to capture the sub-millimeter villous microstructure, the optical scattering behavior, and the luminal folding of native mucosa that together shape its endoscopic appearance. We developed a modular fabrication framework for an anatomically realistic small intestinal phantom with controlled villous microstructure. High-resolution drop-on-demand photopolymer material jetting was used to print discrete patches of villous-like micropillar arrays with tunable height, diameter, and spacing parameterized from histological data spanning Marsh 0 to 3c classifications. The printed patches were then dyed for mucosal-color realism, bonded onto a polyester–spandex substrate, rolled into a continuous tube, and shaped with adjustable retainer rings to introduce luminal folds. Optical microscopy confirmed dimensional fidelity within ±10% of design values with patch-to-patch variation below 7%, and VCE imaging of healthy and atrophic configurations achieved structural similarity (SSIM) values of 0.625 and 0.761 against clinical mucosal imagery. This reproducible platform supports VCE device validation, imaging dataset generation, and clinician training in gastrointestinal imaging. Full article

Surface icing poses a significant risk to unmanned aerial vehicles (UAVs) and compact aerospace platforms, where limited onboard power and space require efficient anti-/de-icing surfaces. In this study, micro/nanostructures were fabricated on TC4 titanium alloy (Ti–6Al–4V) surfaces by femtosecond laser processing at different scanning speeds. The effects of scanning speed on surface morphology, wettability, static freezing, dynamic droplet behavior, and electrothermal de-icing performance were systematically investigated. Increasing the scanning speed induced nonlinear changes in microstructure height and surface roughness, while variations in ablation intensity caused nonuniform material redistribution. The surface processed at 250 mm/s showed the best anti-icing performance, with a water contact angle of 157.5 ± 0.5° and a maximum freezing delay 21.5 times longer than untreated TC4. During electrothermal de-icing, melting initiated at discrete ice–substrate contact points, forming coalesced meltwater films, while interfacial stress concentration promoted crack propagation and rapid ice detachment. Compared with untreated surfaces, ice detachment time (250 mm/s) achieved complete ice detachment at approximately 152 s, whereas ice on the untreated surface remained adhered after 270 s of continuous heating, representing a de-icing time reduction of at least 44%. These results demonstrate that combining laser-fabricated microstructures with electrothermal heating effectively reduces real ice–substrate contact, providing an enhanced anti-/de-icing strategy for lightweight, long-endurance UAV applications under identical electrical input. Full article

This study evaluated the effect of austempering on the microstructure, mechanical properties, and dry-sliding wear performance of EN-GJS-800-8 ductile iron produced as cross-step castings with wall thicknesses of 8, 17, 38, and 48 mm. As-cast and heat-treated specimens were examined by optical microscopy and quantitative image analysis, Brinell hardness, tensile and Charpy impact testing, ball-on-disk testing, and three-dimensional confocal profilometry. Austenitization at 880–890 °C for 2.5 h followed by austempering at 370–380 °C for 2 h produced an optically homogeneous acicular matrix consistent with ausferrite in all investigated sections and reduced the wall-thickness-related variation in hardness. The average hardness reached 296.4 HBW, the ultimate tensile strength 935 MPa, and elongation 8.6%. The mean Charpy impact energy increased from 5.12 to 10.06 J. The wear-track cross-sectional area decreased from approximately 2.98 × 10⁴ to 210 μm², while the maximum track depth decreased from 43.5 to 3 μm. The selected heat-treatment cycle therefore improved strength, impact-energy absorption, and wear resistance while promoting a more uniform response across the casting sections. Full article

This study investigated the development of biopolymer films from bitter cassava starch (Manihot esculenta) and coconut mesocarp cellulose as a promising alternative for biodegradable packaging. The biopolymer film was prepared using the casting method, with glycerol as a plasticiser and Tween 80 as an emulsifier. Different formulations were developed by varying the cellulose concentration to 6%, 8% and 10% to determine how this influences their physical and optical properties. FTIR analysis confirmed the presence of characteristic –OH, C–H, C=O, C–O–C and OH groups in the structure of the cellulose and starch, demonstrating their purity and chemical structure. It was found that the variation in cellulose within the starch polymer matrix significantly influences the microstructural organisation of the material, yielding film thicknesses of between 0.49 and 0.56 mm, with a moisture content ranging from 6.46% to 8.01% and a water absorption percentage between 67.7% and 109.5%; highlighting that the cellulose concentration of 0.4 g (8%) yielded the best results. This research contributes to bridging the existing gap in the utilisation of agricultural waste from bitter cassava and coconut mesocarp, integrating them to form biodegradable composites with potential use in biodegradable packaging, thereby strengthening environmental sustainability through the circular economy. Full article

The Yiyuan jade from Luanchuan County, Henan Province (Central China), has been known since the Neolithic period and provides a scientific reference for tracing the provenance of jade artifacts from nearby Neolithic sites. In this study, the mineralogical characteristics and color genesis of the Yiyuan jade were investigated using petrography, XRD, SEM–EDS, FTIR, UV–Vis–NIR, and EPR spectroscopy. The jade occurs in four color varieties and is petrologically classified as serpentine–bearing dolomitic marble formed by Neoproterozoic gabbroic magma intrusion and subsequent low–temperature alteration. The color variations correspond to distinct mineral assemblages. White jade is dominated by calcite and dolomite; bluish–black jade by antigorite, clinochlore, and chamosite; bluish–white jade contains intermediate proportions of these phases; and green jade consists mainly of epidote and actinolite. The bluish color intensity shows a quantitative correlation with the green mineral content. Bluish–white appears when antigorite and clinochlore together account for 5%–40%, bluish–black when they exceed 40%, and bluish–gray when chamosite exceeds 10%. The bluish–black coloration is controlled by the dense fibrous interwoven microstructure of antigorite rather than by Fe or other elemental chromophores. These distinctive features serve as diagnostic criteria for identifying bluish–black jade materials from Neolithic sites in the Luanchuan region. Full article

Resistance spot welding (RSW) is the primary joining technology for automotive advanced high-strength steels (AHSSs), where the inherent severe thermal cycles profoundly alter the heat-affected zone (HAZ) microstructure, leading to localized variations in mechanical properties. Characterizing the spatial gradients in microstructure and the resulting mechanical properties remains a major challenge in weld failure analysis due to the small size of the HAZ and its complex thermal history. In this study, the HAZ of two prominent AHSS grades, a first-generation press hardening steel (PHS1500) and a third-generation quenching and partitioning steel (Q&P1180), was physically simulated using a Gleeble^® 3180 thermomechanical simulator to achieve precise control over the localized thermal cycles. The investigation first evaluated the role of thermal cycle duration, governed by the welding time parameter (300 ms vs. 800 ms), on the microstructural evolution of the PHS1500 steel. Increasing the weld time from 300 ms to 800 ms reduced the cooling rate under the nominal 1400 °C condition from approximately 3000 K/s to 2500 K/s; however, no marked change was observed in the overall microstructural and hardness trends within the investigated range. Subsequently, using the 300 ms thermal profile as a reference baseline, a comparative metallurgical study was conducted between PHS1500 and Q&P1180. Under the same 300 ms thermal history, the maximum hardness reduction relative to the corresponding base material was approximately 42% for PHS1500 and 12% for Q&P1180. The hardness minima were located within FE-estimated temperature ranges close to the Ac₁ region for PHS1500 and around 600 °C for Q&P1180, respectively. This comparison highlighted the distinct microstructural responses of the two generations across the upper-critical (UCHAZ), inter-critical (ICHAZ), and sub-critical (SCHAZ) zones. Moreover, microhardness profiles were correlated with the microstructural findings, establishing a correlation among the simulated thermal history, the observed microstructural evolution, and localized mechanical performance. Full article

At present, the detection methods for the microstructure and mechanical properties of aluminum alloys are mainly based on SEM, EBSD, TEM, tensile tests, and microhardness tests, which are time-consuming and destructive. In this paper, laser ultrasonic non-destructive detection is employed to obtain ultrasonic signals from Al-Cu-Mg aluminum alloy subjected to various heat treatment processes. The results reveal empirical correlations between the characteristic values of the ultrasonic signals and the material’s state. Specifically, the characteristic values exhibit an inverse correlation with the precipitated phase content. When both the precipitated phase content and the average grain size vary significantly, distinct deviations in the characteristic values are observed, which can serve as indicators of microstructural changes. The extracted ultrasonic eigenvalues also show promising, empirically derived correlations with mechanical properties, with frequency-domain attenuation coefficients demonstrating relatively higher sensitivity based on fitting analyses within the current dataset. These observed variations are tentatively discussed as plausible consequences of grain boundary scattering and changes in matrix solid solution strengthening associated with precipitate dissolution. Overall, the findings suggest the potential of laser ultrasonics as a rapid non-destructive evaluation tool, providing a preliminary scientific basis for further development of methods to assess the microstructure and mechanical properties of Al-Cu-Mg alloys within the tested parameter space. Full article

Laser powder bed fusion (LPBF)-fabricated TA15 titanium alloy commonly exhibits a fine acicular lath morphology, which has frequently been interpreted as martensitic in previous studies and is generally associated with high strength and limited plastic accommodation. In this study, LPBF-TA15 specimens were annealed at 800, 900, and 950 °C for 2 h, followed by furnace cooling, and subsequently subjected to secondary annealing at 550 °C for 4 h. Each sequentially annealed condition was compared with its corresponding single-step condition to distinguish retained microstructural differences from the tensile-property changes associated with the subsequent treatment. Microstructural evolution and monotonic tensile properties at room temperature and 300–600 °C were investigated. Annealing at 800 °C retained a relatively fine lamellar morphology. Increasing the initial annealing temperature to 900 and 950 °C produced progressively larger apparent lath and colony scales, with the most pronounced coarsening observed at 950 °C. Tensile results are reported as mean ± standard deviation. After secondary annealing, A800-S550 exhibited the highest mean room-temperature strength among the three secondary-annealed conditions, with a yield strength of 1045.0 ± 2.6 MPa, an ultimate tensile strength of 1116.7 ± 2.3 MPa, and an elongation of 14.3 ± 0.7%. From 300 to 600 °C, its yield strength decreased from 701.0 ± 3.2 to 493.6 ± 9.8 MPa, while its ultimate tensile strength decreased from 823.5 ± 3.8 to 585.6 ± 7.1 MPa; the elongation at 600 °C was 19.0 ± 1.8%. In this study, microstructural inheritance refers to the persistence, after the common 550 °C treatment, of differences in lath and lamellar-colony scales and EBSD boundary characteristics established during initial annealing. The secondary-annealed conditions retained distinct microstructural scales and exhibited different tensile responses; however, a unique causal relationship between the retained morphology and the magnitude of the property changes was not established. Residual stress, post-heat-treatment oxygen variation, and quantitative texture evolution were not independently evaluated. The conclusions are limited to the heat-treatment schedules and monotonic tensile conditions examined in this study. Full article

The role of the Zn/Mg ratio in regulating microstructure, precipitation evolution and coarsening resistance in Al–Zn–Mg-based alloys was investigated by microhardness testing, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) during isothermal aging at 150 °C. Three alloy compositions were designed with Zn/Mg ratios of 1.6, 2.4, and 3.9, whereas the combined Zn and Mg level was fixed at 6.0 wt%. All alloys exhibited a typical age-hardening response, whereas the maximum peak hardness was obtained at an intermediate Zn/Mg level rather than at the two extremes. The optimal composition (Zn/Mg = 2.4) reached 137 HV, which is attributable to the formation of the finest precipitates (~3 nm) and the highest number density. Moreover, this alloy exhibited the smallest hardness loss (ΔH = 19 HV) after prolonged aging (192 h). TEM analysis indicated that this alloy exhibited the lowest coarsening rate constant, Kr = 0.43 at 192 h. Furthermore, the variation in Zn/Mg ratio affected grain boundary precipitation, leading to a minimized PFZ width at Zn/Mg = 2.4 while maintaining a similar discontinuous distribution of grain boundary precipitates among the alloys. Overall, tailoring the Zn/Mg balance offers an effective strategy to achieve refined precipitates, improved coarsening resistance, and enhanced mechanical performance with superior thermal stability. Full article

A multicomponent Ni₅₄Cr₂₈Mo₈Nb₅Ta₅ nickel-based superalloy was produced by vacuum induction melting followed by homogenization, hot forging, solution treatment, and aging to investigate its microstructural and mechanical behavior. The X Ray Fluorescence (XRF) analysis confirmed excellent agreement between the nominal and experimental chemical compositions. The X Ray Diffraction(XRD) combined with Rietveld refinement revealed a microstructure dominated by three closely related to face-centered cubic (FCC) (A1) solid-solution regions with slightly different lattice parameters, indicating local compositional variations. The Scanning Electron Microscopy(SEM)/Energy Dispersive Spectroscopy (EDS) observations showed a generally homogeneous elemental distribution, while optical and electron microscopy identified a dendritic microstructure with elongated interdendritic constituents enriched in refractory elements. Mechanical characterization yielded an average hardness of 497 HV_0.5, a compressive strength of approximately 1950 MPa, and room-temperature yield and ultimate tensile strengths of 1050 MPa and 1320 MPa, respectively. Tensile strength gradually decreased with increasing temperature up to 900 °C, while ductility increased from 16% to 25% total elongation. The results indicate that the alloy develops a stable FCC matrix primarily strengthened by solid-solution hardening, with the measured mechanical performance suggesting an additional contribution from precipitation hardening. This study provides an experimental baseline for the development and optimization of conventionally processed Ni–Cr–Mo–Nb–Ta superalloys for high-temperature applications. Full article

This study focuses on how modulating the electrical pulse frequency alters both the topographic features and corrosion resistance of ceramic coatings produced via micro-arc oxidation (MAO) on an AZ31B magnesium substrate. In a silicate-based electrolyte, MAO treatments were executed utilizing four distinct frequencies: 300, 500, 800, and 1000 Hz. Phase configurations, microstructural features, and surface patterns were thoroughly evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM) integrated with energy dispersive spectroscopy (EDS), and an ultra-depth-of-field microscope. Furthermore, the fabricated coatings underwent rigorous assessments for their porosity, contact angle, Vickers hardness, and electrochemical attributes. The outcomes demonstrate that the surface appearance, phase structure, defect state, and density of the MAO coatings are highly sensitive to variations in pulse frequency. Notably, although the coating prepared at 800 Hz exhibited elevated surface roughness (Ra), it achieved a highly consolidated microstructure and the lowest porosity level, underscoring that roughness alone is not a definitive quality indicator. This structural refinement was driven by the presence of well-crystallized Mg₂SiO₄ and MgO phases. This group recorded a peak inner barrier layer resistance (R_b) of 1.62 × 10⁴ Ω·cm² alongside a minimum corrosion current density (I_corr) of 3.38 × 10⁻⁷ A·cm⁻², confirming its exceptional protective capacity. Consequently, the structural quality and corrosion resistance of MAO coatings can be strategically enhanced by tuning the electrical frequency, offering valuable engineering guidelines for utilizing AZ31B alloy parts under aggressive environmental conditions. Full article

Deoxidized high-phosphorus (DHP) copper is widely used in marine heat-exchangers and seawater piping, where long-term structural reliability demands both high strength and a deformation-tolerant microstructure to resist damage initiation. Constrained groove pressing (CGP) is a scalable severe plastic deformation route for metallic sheets; however, the sharp trapezoidal junctions of the conventional die impose parasitic bending strains that produce sinusoidal in-plane hardness variations and anisotropic properties. This study introduces a modified CGP (MCGP) process in which the sharp crest and valley of each 45° tooth are replaced by tangent circular arcs (R₁ = 1.6 mm at the crest, R₂ = 4.8 mm at the valley), removing geometric discontinuities while exactly preserving the groove angle, pitch, and die envelope for drop-in compatibility with existing equipment. DHP copper sheets processed by conventional CGP and MCGP were systematically compared using optical microscopy, SEM, XRD, microhardness, tensile testing, and finite-element analysis. MCGP delivered exceptional mechanical performance: yield strength of 281.19 MPa, ultimate tensile strength of 451.94 MPa (96.4% above the as-received state and 23.8% above conventional CGP), mean hardness of 131.38 HV, and the finest apparent (instrument-uncalibrated) coherent diffraction-domain size of 22.75 nm. Finite-element modelling revealed a lower peak equivalent plastic strain with a more continuously distributed through-thickness deformation path, despite an unchanged nominal grooving strain (≈0.56). Notably, while the modified die redistributes deformation rather than amplifying the nominal strain, the measured through-thickness hardness inhomogeneity factor increased from 7.14% to 21.97% due to strain concentration in the mid-thickness region, indicating that full homogenisation requires further arc-radius optimisation. Nevertheless, the substantial gains in strength and microstructural refinement demonstrate that MCGP offers a promising processing route for producing DHP copper components with enhanced strength and refined microstructures, which may contribute to improved damage tolerance. However, it is acknowledged that direct tests on seawater corrosion, corrosion fatigue, and thermal cycling were not performed in this study; the implications for marine service life are inferred from the established literature on the benefits of grain refinement for corrosion and fatigue resistance. Future work incorporating marine environmental performance tests is recommended to validate these implications. Full article